Re: [PATCH 2/3] KVM: nVMX: Fix fail to get nested ack intr's vector during nested vmexit

Wanpeng Li
2014-07-17T10:03:16Z

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On Thu, Jul 17, 2014 at 09:13:56AM +0000, Zhang, Yang Z wrote:
>Paolo Bonzini wrote on 2014-07-17:
>> Il 17/07/2014 06:56, Wanpeng Li ha scritto:
>>> && nested_exit_intr_ack_set(vcpu)) {
>>> int irq = kvm_cpu_get_interrupt(vcpu);
>>> +
>>> + if (irq < 0 && kvm_apic_vid_enabled(vcpu->kvm))
>>> + irq = kvm_get_apic_interrupt(vcpu);
>>
>> There's something weird in this patch. If you "inline"
>> kvm_cpu_get_interrupt, what you get is this:
>>
>> int irq;
>> /* Beginning of kvm_cpu_get_interrupt... */
>> if (!irqchip_in_kernel(v->kvm))
>> irq = v->arch.interrupt.nr;
>> else {
>> irq = kvm_cpu_get_extint(v); /* PIC */
>> if (!kvm_apic_vid_enabled(v->kvm) && irq == -1)
>> irq = kvm_get_apic_interrupt(v); /* APIC */
>> }
>>
>> /* kvm_cpu_get_interrupt done. */
>> if (irq < 0 && kvm_apic_vid_enabled(vcpu->kvm))
>> irq = kvm_get_apic_interrupt(vcpu);
>>
>> There are just two callers of kvm_cpu_get_interrupt, and the other is
>> protected by kvm_cpu_has_injectable_intr so it won't be executed if
>> virtual interrupt delivery is enabled. So you patch is effectively the same as this:
>>
>> diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c index
>> bd0da43..a1ec6a5 100644 --- a/arch/x86/kvm/irq.c +++
>> b/arch/x86/kvm/irq.c @@ -108,7 +108,7 @@ int
>> kvm_cpu_get_interrupt(struct kvm_vcpu *v)
>>
>> vector = kvm_cpu_get_extint(v);
>> - if (kvm_apic_vid_enabled(v->kvm) || vector != -1)
>> + if (vector != -1)
>> return vector; /* PIC */
>>
>> return kvm_get_apic_interrupt(v); /* APIC */
>> But in kvm_get_apic_interrupt I have just added this comment:
>>
>> /* Note that we never get here with APIC virtualization
>> * enabled. */
>>
>> because kvm_get_apic_interrupt calls apic_set_isr, and apic_set_isr
>> must never be called with APIC virtualization enabled either. With
>> APIC virtualization enabled, isr_count is always 1, and
>> highest_isr_cache is always -1, and apic_set_isr breaks both of these invariants.
>>
>
>You are right. kvm_lapic_find_highest_irr should be the right one.
>

That is my original proposal solution of this bug. However, what I concern
after more think is since kvm_lapic_find_highest_irr will not clear irr,
if the intr will be injected by kvm_86_ops->hwapic_irr_update(vcpu,
kvm_lapic_find_highest_irr(vcpu)) which called by vcpu_enter_guest()
again?

Any idea, Paolo?

Regards,
Wanpeng Li

>> Paolo
>
>
>Best regards,
>Yang
>

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>From b14c444e073a21560961b37be643b78c6c9cba17 Mon Sep 17 00:00:00 2001
From: Wanpeng Li <wanpeng.li@linux.intel.com>
Date: Thu, 17 Jul 2014 17:41:28 +0800
Subject: [PATCH v2] KVM: nVMX: Fix fail to get nested ack intr's vector during nested vmexit

WARNING: CPU: 9 PID: 7251 at arch/x86/kvm/vmx.c:8719 nested_vmx_vmexit+0xa4/0x233 [kvm_intel]()
Modules linked in: tun nfsv3 nfs_acl auth_rpcgss oid_registry nfsv4 dns_resolver nfs fscache lockd
sunrpc pci_stub netconsole kvm_intel kvm bridge stp llc autofs4 8021q ipv6 uinput joydev microcode
pcspkr igb i2c_algo_bit ehci_pci ehci_hcd e1000e ixgbe ptp pps_core hwmon mdio i2c_i801 i2c_core
tpm_tis tpm ipmi_si ipmi_msghandler isci libsas scsi_transport_sas button dm_mirror dm_region_hash
dm_log dm_mod
CPU: 9 PID: 7251 Comm: qemu-system-x86 Tainted: G W 3.16.0-rc1 #2
Hardware name: Intel Corporation S2600CP/S2600CP, BIOS RMLSDP.86I.00.29.D696.1311111329 11/11/2013
000000000000220f ffff880ffd107bf8 ffffffff81493563 000000000000220f
0000000000000000 ffff880ffd107c38 ffffffff8103f0eb ffff880ffd107c48
ffffffffa059709a ffff881ffc9e0040 ffff8800b74b8000 00000000ffffffff
Call Trace:
[<ffffffff81493563>] dump_stack+0x49/0x5e
[<ffffffff8103f0eb>] warn_slowpath_common+0x7c/0x96
[<ffffffffa059709a>] ? nested_vmx_vmexit+0xa4/0x233 [kvm_intel]
[<ffffffff8103f11a>] warn_slowpath_null+0x15/0x17
[<ffffffffa059709a>] nested_vmx_vmexit+0xa4/0x233 [kvm_intel]
[<ffffffffa0594295>] ? nested_vmx_exit_handled+0x6a/0x39e [kvm_intel]
[<ffffffffa0537931>] ? kvm_apic_has_interrupt+0x80/0xd5 [kvm]
[<ffffffffa05972ec>] vmx_check_nested_events+0xc3/0xd3 [kvm_intel]
[<ffffffffa051ebe9>] inject_pending_event+0xd0/0x16e [kvm]
[<ffffffffa051efa0>] vcpu_enter_guest+0x319/0x704 [kvm]

After commit 77b0f5d (KVM: nVMX: Ack and write vector info to intr_info if L1
asks us to), "Acknowledge interrupt on exit" behavior can be emulated. Current
logic will ask for intr vector if it is nested vmexit and VM_EXIT_ACK_INTR_ON_EXIT
is set by L1. However, intr vector for posted intr can't be got by generic read
pending interrupt vector and intack routine, there is a requirement to sync from
pir to irr. This patch fix it by ask the intr vector after sync pir to irr.

Signed-off-by: Wanpeng Li <wanpeng.li@linux.intel.com>
---
v1 -> v2:
* replace kvm_get_apic_interrupt() by kvm_lapic_find_highest_irr()

arch/x86/kvm/lapic.c | 1 +
arch/x86/kvm/vmx.c | 3 +++
2 files changed, 4 insertions(+)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 0069118..b7d45dc 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -1637,6 +1637,7 @@ int kvm_get_apic_interrupt(struct kvm_vcpu *vcpu)
apic_clear_irr(vector, apic);
return vector;
}
+EXPORT_SYMBOL_GPL(kvm_get_apic_interrupt);

void kvm_apic_post_state_restore(struct kvm_vcpu *vcpu,
struct kvm_lapic_state *s)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 4ae5ad8..a704f71 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -8697,6 +8697,9 @@ static void nested_vmx_vmexit(struct kvm_vcpu *vcpu, u32 exit_reason,
if ((exit_reason == EXIT_REASON_EXTERNAL_INTERRUPT)
&& nested_exit_intr_ack_set(vcpu)) {
int irq = kvm_cpu_get_interrupt(vcpu);
+
+ if (irq < 0 && kvm_apic_vid_enabled(vcpu->kvm))
+ irq = kvm_lapic_find_highest_irr(vcpu);
WARN_ON(irq < 0);
vmcs12->vm_exit_intr_info = irq |
INTR_INFO_VALID_MASK | INTR_TYPE_EXT_INTR;
--
1.9.1